Some disk array enclosures use hard disk drives that require 12 volts DC only, and the midplane (or backplane) to which such disk drives are electrically connected provides the requisite voltage (i.e., 12 volts only). Additionally, some disk array enclosures use hard disk drives with customized features that enhance their suitability within a product. These features include, but are not limited to, on/off control, soft-start control, current-limit protection, and logic signal conditioning. To reduce the cost of disk array enclosures, one trend is to use commodity (i.e., off-the-shelf) disk drives. Commodity disk drives, however, can require more than a single voltage level, such as 12 volts DC and 5 volts DC. These disk drives may also lack the prerequisite enhanced features needed to make them suitable in a particular application or product. To use such commodity disk drives in these disk array enclosures therefore requires means, external to the disk drive, for converting the 12 volts supplied by the midplane into each required voltage level, for producing certain system functionality (e.g., the enhanced features), or both.
To perform this voltage conversion (and various system functionality, such as previously described), an external, small circuit card (also called a paddle card or an adapter board) is disposed between the midplane and the disk drive. This circuit card includes electrical signal paths and circuitry, e.g., for delivering a 5-volt and 12-volt supply to the disk drive based on the 12-volt supply provided by the midplane, for passing through the 12 volts from the midplane to meet the 12-volts requirements of the disk drive, and for providing the various enhanced functionality.